This invention relates generally to the manufacture of ophthalmic lenses and more particularly concerns blocks used for mounting ophthalmic lenses on lens generating, fining, polishing and edging machines.
In a typical lens blocking process, the lens is marked for blocking and protective tape is applied to its front surface. A block covering the entire surface of the lens is applied to the tape. An alloy pumped in a liquid state fills the gaps or voids between the tape and the block. When blocking is completed, the lens goes through the generating and fining/polishing processes. The block is then removed from the lens by shocking the block to break its bond to the tape. After the lens is cleaned and inspected, it must be reblocked for edging using a much smaller diameter block than the block used in the generating and fining/polishing steps. Blocking for edging is generally accomplished by inserting a double-sided adhesive pad between the block and the lens. After the lens has been edged, the block is removed by twisting the block to break the adhesion.
The above process is very expensive and inefficient. Twice blocking the lens is a time consuming and tedious operation. Alloy injection is costly and time consuming. It necessitates additional equipment for heating and injecting the alloy into the void. It causes a delay in the process until the alloy has sufficiently cooled and solidified. The alloy reclamation process is also costly and time consuming, requiring the alloy to be reheated to liquification for collection. Additional equipment is also required for its reclamation from the lens. Moreover, the use of alloys in the process will likely be discontinued since some of them contain cadmium and lead, materials which may be banned by governmental agencies due to health considerations.
While it is desirable to eliminate the need for multiple blocking steps and the use of an alloy which must be liquified for injection and again liquified for retrieval, the lens making process complicates possible solutions to these problems. The lens generating, fining and polishing steps result in the application of forces to the face of the lens which may cause the lens to flex and distort. Consequently, the block and chuck used in these steps must sufficiently complement and support the surface of the lens so as to prevent this deflection or distortion. On the other hand, the block used in the lens edging step of the process must be sufficiently small so that the edging equipment will not come into contact with the block. This is why presently known lens edging blocks are significantly smaller than presently known lens generating blocks.
It is, therefore, an object of this invention to provide a single lens block suitable for use during the entire lens making process. Another object of this invention is to provide a single lens block that is easily modified from a lens generating and polishing/fining configuration to an edging configuration. Another object of this invention is to provide a lens block which provides support for the front face of a lens against cutting forces applied to the lens as it is being generated, fined and polished. Yet another object of this invention is to provide a lens block which consists of a quick curing or instant adhesive.